Defects in Nucleotide Excision Repair (NER) have been linked directly to numerous human diseases including xeroderma pigmentosum, Cockayne syndrome and cancer. The mechanism of DNA damage recognition remains poorly understood in all cellular models. A central feature to the conundrum of damage recognition is whether localized distortion of the DNA duplex, possibly by the unpairing of base pairs near the damage site, is the crucial step enabling a site of DNA damage to be identified and subsequently removed by the NER machinery. If the unpairing of base pairs near the damage site is truly a crucial feature in identifying damage then it follows directly that sequences immediately surrounding any form of damage will bear on the damage recognizability, i.e. sequences that unpair more easily should be more easily recognized. The proposed study has two goals. The primary goal will be to determine in Saccharomyces cerevesiae if here is a DNA sequence context preference for recognition of two types of DNA damage known to be repaired exclusively by NER:2-acetylaminofluorene-DNA adducts and benzo[a]pyrene diol epoxide-DNA adducts. The recognizability of both forms of damage will be compared within a panel of DNA substrates that differ in the sequence context of the damage site. The secondary goal of this project is to make a correlation with the NER proteins themselves by identifying specifically which protein components within the NER machinery give rise to any observed sequence context preference.